Systems and methods for reducing non-linearities of a microphone signal

ABSTRACT

To correct for non-linearities in the response of a microphone as a function of sound pressure level incident upon the microphone, a displacement non-linearity function is applied to the signal path of the microphone, wherein the displacement non-linearity function is a function of the digital audio output signal and has a response modeling non-linearities of the displacement as a function of a sound pressure level incident upon the microphone.

RELATED APPLICATIONS

The present disclosure claims priority to U.S. Provisional PatentApplication Ser. No. 61/810,075, filed Apr. 9, 2013, which isincorporated by reference herein in its entirety.

FIELD OF DISCLOSURE

The present disclosure relates in general to audio systems, and moreparticularly, to reducing distortion of a microphone signal.

BACKGROUND

Microphones are ubiquitous on many devices used by individuals,including computers, tablets, smart phones, and many other consumerdevices. Generally speaking, a microphone is an electroacoustictransducer that produces an electrical signal in response to deflectionof a portion (e.g., a membrane or other structure) of a microphonecaused by sound incident upon the microphone.

Traditionally, it has often been assumed that operation of a microphoneis linear, such that the electrical signal generated by a microphone isa linear function of the sound pressure level incident upon themicrophone. However, a microphone may operate with many non-linearities,including non-linear relationships of deflection as a function of soundpressure level. Left uncorrected, such non-linearities may causedistortion, in that the audio signal generated from a microphone may notbe accurately representative of the actual sound incident upon themicrophone.

SUMMARY

In accordance with the teachings of the present disclosure, certaindisadvantages and problems associated with non-linear distortion of amicrophone signal may be reduced or eliminated.

In accordance with embodiments of the present disclosure, a system mayinclude a processor configured to couple to an audio transducer having adigital audio output signal indicative of audio sounds incident upon theaudio transducer, wherein the digital audio output signal is a functionof a displacement associated with the audio transducer. The processormay also be configured to, based on the digital audio output signal or aderivative thereof and a displacement non-linearity function associatedwith the audio transducer, generate a modified digital audio outputsignal, wherein the displacement non-linearity function is a function ofthe digital audio output signal and has a response modelingnon-linearities of the displacement as a function of a sound pressurelevel incident upon the audio transducer.

In accordance with these and other embodiments of the presentdisclosure, a method may include receiving from an audio transducer adigital audio output signal indicative of audio sounds incident upon theaudio transducer, wherein the digital audio output signal is a functionof a displacement associated with the audio transducer. The method mayalso include, based on the digital audio output signal or a derivativethereof and a displacement non-linearity function associated with theaudio transducer, generating a modified digital audio output signal,wherein the displacement non-linearity function is a function of thedigital audio output signal and has a response modeling non-linearitiesof the displacement as a function of a sound pressure level incidentupon the audio transducer.

Technical advantages of the present disclosure may be readily apparentto one having ordinary skill in the art from the figures, descriptionand claims included herein. The objects and advantages of theembodiments will be realized and achieved at least by the elements,features, and combinations particularly pointed out in the claims.

It is to be understood that both the foregoing general description andthe following detailed description are explanatory examples and are notrestrictive of the claims set forth in this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments and advantagesthereof may be acquired by referring to the following description takenin conjunction with the accompanying drawings, in which like referencenumbers indicate like features, and wherein:

FIG. 1 illustrates a block diagram of selected components of an exampleaudio system, in accordance with embodiments of the present disclosure;

FIG. 2 illustrates a block diagram of selected components of a digitalmicrophone integrated circuit, in accordance with embodiments of thepresent disclosure; and

FIG. 3 illustrates a block diagram of selected functional blocks of adigital audio processor, in accordance with embodiments of the presentdisclosure.

DETAILED DESCRIPTION

FIG. 1 illustrates a block diagram of selected components of an exampleaudio system 100, in accordance with embodiments of the presentdisclosure. As shown in FIG. 1, audio system 100 may include amicrophone transducer 101, a digital microphone integrated circuit (IC)105, and a digital audio processor 109. Microphone transducer 101 maycomprise any system, device, or apparatus configured to convert soundincident at microphone transducer 101 to an electrical signal, forexample analog output signal 103, wherein such sound is converted to anelectrical signal using a diaphragm or membrane having an electricalcapacitance that varies as based on sonic vibrations received at thediaphragm or membrane. Microphone transducer 101 may include anelectrostatic microphone, a condenser microphone, an electretmicrophone, a microelectromechanical systems (MEMs) microphone, or anyother suitable capacitive microphone.

Digital microphone IC 105 may comprise any suitable system, device, orapparatus configured to process analog output signal 103 to generate adigital audio output signal 107 and condition digital audio outputsignal 107 for transmission over a bus to digital audio processor 109.Once converted to digital audio output signal 107, the audio signal maybe transmitted over significantly longer distances without beingsusceptible to noise as compared to an analog transmission over the samedistance. In some embodiments, digital microphone IC 105 may be disposedin close proximity with microphone transducer 101 to ensure that thelength of the analog line between microphone transducer 101 and digitalmicrophone IC 105 is relatively short to minimize the amount of noisethat can be picked up on an analog output line carrying analog outputsignal 103. For example, in some embodiments, microphone transducer 101and digital microphone IC 105 may be formed on the same integratedcircuit die or substrate.

Digital audio processor 109 may comprise any suitable system, device, orapparatus configured to process digital audio output signal 107 for usein a digital audio system. For example, digital audio processor 109 maycomprise a microprocessor, microcontroller, digital signal processor(DSP), application specific integrated circuit (ASIC), or any otherdevice configured to interpret and/or execute program instructionsand/or process data, such as digital audio output signal 107.

FIG. 2 illustrates a block diagram of selected components of digitalmicrophone IC 105, in accordance with embodiments of the presentdisclosure. As shown in FIG. 2, digital microphone IC 105 may include apre-amplifier 203, an analog-to-digital converter (ADC) 215, and adriver 219. Pre-amplifier 203 may receive analog output signal 103 viaone or more input lines 201 which may allow for receipt of asingle-ended signal, differential signal, or any other suitable analogaudio signal format and may comprise any suitable system, device, orapparatus configured to condition analog output signal 103 forprocessing by ADC 215. The output of pre-amplifier 203 may becommunicated to ADC 215 on one or more output lines 205.

ADC 215 may comprise any suitable system device or apparatus configuredto convert an analog audio signal received at its input, to a digitalsignal representative of analog output signal 103. ADC 215 may itselfinclude one or more components (e.g., delta-sigma modulator, decimator,etc.) for carrying out the functionality of ADC 215.

Driver 219 may receive the digital signal output by ADC 215 and maycomprise any suitable system, device, or apparatus configured tocondition such digital signal (e.g., encoding into AES/EBU, S/PDIF, orother suitable audio interface standards), in the process generatingdigital audio output signal 107 for transmission over a bus to digitalaudio processor 109. In FIG. 2, the bus receiving digital audio outputsignal 107 is shown as single-ended. In some embodiments, driver 219 maygenerate a differential digital audio output signal 107.

FIG. 3 illustrates a block diagram of selected functional blocks of adigital audio processor 109, in accordance with embodiments of thepresent disclosure. As shown in FIG. 3, digital audio processor 109 mayinclude a filter with a response F(x(t)). Response F(x(t)) is amicrophone non-linearity function that is a function of digital outputaudio signal 107 (represented by x(t) in FIG. 3) and modelsnon-linearities of the displacement of microphone transducer 101 as afunction of a sound pressure level incident upon microphone transducer101. For example, response F(x(t)) may combine non-linearities (e.g.,force factor, stiffness) of microphone 101 into a single scaling factorwhich is a function of a digital audio signal x(t). Accordingly,responsive to digital audio output signal 107 (x(t)), filter 302 maygenerate a modified digital audio output signal 304 (x′(t)).

In some embodiments, microphone non-linearity function F(x(t)) may becharacterized using offline testing of one or more microphones similarto the microphone transducer 101. For example, in such embodiments,microphone non-linearity function F(x(t)) may be determined by observingan actual digital audio output signal x(t) in response to a particularsound (e.g., pink noise) incident on microphone transducer 101 todetermine any non-linear response of the digital audio output signal tothe incident sound. In addition or alternatively, such testing may beapplied to many microphones similar or identical in design to microphonetransducer 101 (e.g., the same model as microphone transducer 101), suchthat response F(x(t)) is based on an average of similar or identicalmicrophone transducers.

This disclosure encompasses all changes, substitutions, variations,alterations, and modifications to the example embodiments herein that aperson having ordinary skill in the art would comprehend. Similarly,where appropriate, the appended claims encompass all changes,substitutions, variations, alterations, and modifications to the exampleembodiments herein that a person having ordinary skill in the art wouldcomprehend.

Moreover, reference in the appended claims to an apparatus or system ora component of an apparatus or system being adapted to, arranged to,capable of, configured to, enabled to, operable to, or operative toperform a particular function encompasses that apparatus, system, orcomponent, whether or not it or that particular function is activated,turned on, or unlocked, as long as that apparatus, system, or componentis so adapted, arranged, capable, configured, enabled, operable, oroperative.

All examples and conditional language recited herein are intended forpedagogical objects to aid the reader in understanding the disclosureand the concepts contributed by the inventor to furthering the art, andare construed as being without limitation to such specifically recitedexamples and conditions. Although embodiments of the present disclosurehave been described in detail, it should be understood that variouschanges, substitutions, and alterations could be made hereto withoutdeparting from the spirit and scope of the disclosure.

What is claimed is:
 1. A system comprising: a processor configured to:couple to an audio transducer having a digital audio output signalindicative of audio sounds incident upon the audio transducer, whereinthe digital audio output signal is a function of a displacementassociated with the audio transducer; and based on the digital audiooutput signal or a derivative thereof and a displacement non-linearityfunction associated with the audio transducer, generate a modifieddigital audio output signal, wherein the displacement non-linearityfunction is a function of the digital audio output signal and has aresponse modeling non-linearities of the displacement as a function of asound pressure level incident upon the audio transducer.
 2. The systemof claim 1, wherein the audio transducer comprises a microphone.
 3. Thesystem of claim 2, wherein the microphone comprises amicroelectromechanical systems microphone.
 4. The system of claim 1,wherein the displacement non-linearity function is based on offlinetesting of one or more audio transducers similar to the audiotransducer.
 5. The system of claim 1, wherein the digital audio inputsignal is a digital signal based on an analog signal generated by theaudio transducer.
 6. A method comprising: receiving from an audiotransducer a digital audio output signal indicative of audio soundsincident upon the audio transducer, wherein the digital audio outputsignal is a function of a displacement associated with the audiotransducer; and based on the digital audio output signal or a derivativethereof and a displacement non-linearity function associated with theaudio transducer, generating a modified digital audio output signal,wherein the displacement non-linearity function is a function of thedigital audio output signal and has a response modeling non-linearitiesof the displacement as a function of a sound pressure level incidentupon the audio transducer.
 7. The method of claim 6, wherein the audiotransducer comprises a microphone.
 8. The method of claim 7, wherein themicrophone comprises a microelectromechanical systems microphone.
 9. Themethod of claim 6, wherein the displacement non-linearity function isbased on offline testing of one or more audio transducers similar to theaudio transducer.
 10. The method of claim 6, wherein the digital audioinput signal is a digital signal based on an analog signal generated bythe audio transducer.